For Honeycomb, we added proper file thread-safety for
all FILE* operations. However, we did implement that by
using an out-of-band hash table to map FILE* pointers
to phtread_mutex_t mutexes, because we couldn't change
the size of 'struct _sFILE' without breaking the ABI.
It turns out that our BSD-derived code already has
some support code to extend FILE* objects, so use it
instead. See libc/stdio/fileext.h
This patch gets rid of the hash table, and put the
mutex directly into the sFILE extension.
Change-Id: If1c3fe0a0a89da49c568e9a7560b7827737ff4d0
